What is the name of the filamentous structure that may form the primary part of the fungal organism?

The filamentous structure that forms the primary part of a fungal organism is called mycelium. Mycelium is composed of a network of microscopic filaments known as hyphae, which grow and spread out in various directions. Together, these hyphae create the mycelium, which serves as the main vegetative body of the fungus. The mycelium is crucial for nutrient absorption as it effectively increases the surface area for taking in nutrients from the environment.

While hyphae are the individual threads that make up the mycelium, referring to the entire network collectively identifies it as mycelium. Other terms such as thallus and rhizoid refer to different types of structures in other organisms or specific functions but are not used to describe the primary structure of fungi.